The present invention is directed to a tool bit for insertion into a tool bit chuck in a manually operated tool used for chiseling and/or percussion drilling and having a chucking shank with at least two axially extending rotary entrainment grooves open at the end of the shank inserted into the chuck and at least one locking groove closed at its ends extending transversely of the axial direction and located in the outside surface of the shank between the rotary entrainment grooves.
Tool bits for manually operated tools are disclosed in DE-PS 25 51 125 with the chucking shank of these tool bits having one or two locking grooves closed at the ends extending transversely of the axial direction along with one or two rotary entrainment grooves open at the end of the shank inserted into the chuck. The tool bit chuck into which the tool bits are inserted has one or two radially displaceable locking elements in the form of balls, however, it is known to use rollers instead of balls for the locking elements. By engagement of the locking elements in the locking grooves, a positively locked connection is established for the tool bit in the tool bit chuck. Such a positively locked connection can be released by a radially outward displacement of the locking element, whereby the tool bit can be removed from the chuck. Since the rotary entrainment grooves in the tool bit cooperate with entrainment strips in the tool bit chuck for effecting the transmission of torque from the chuck to tool bit, especially high loads are not applied in the locking grooves cooperating with the locking elements. It is only when the tool bits are pulled from a bore in a structural part that certain axial forces must be transmitted by the locking grooves in cooperation with the locking elements for assuring that the connection between the tool bit and the tool bit chuck is maintained.
A very high load or stress is applied to the rotary entrainment grooves open at the end of the chucking shank inserted into the chuck which engage with matching entrainment strips in the chuck. Such high stress is a result of the torque transmitted from the tool bit chuck to the tool bit. This torque increases with an increase in the diameter of the working region of the tool bits being used.
Due to present trends where tool bits with larger diameters in the working region are increasingly being used in manually operated tools, a considerable wear phenomenon occurs in the rotary entrainment grooves due to the very great torques to be transmitted and a premature failure of the tool bits may occur. Such premature failure caused by the rotary entrainment grooves may take place before the normal wear caused by conventional use is reached in the working region of the tool bit.